The present invention relates to a contactless IC card for receiving power and for receiving/transmitting signals from/to a reader/writer as an upper terminal by electromagnetic coupling. More particularly, the invention relates to the structure of an antenna coil in the contactless IC card.
In recent years, attention has been paid to an IC card having therein an IC such as a processor as a storage medium of electronic money or the like. There are two types of IC cards according to different signal transmitting methods. One is a contact IC card which receives power and clocks from a reader/writer as an upper terminal by using a contact point and processes a command from the reader/writer. The other is a contactless IC card 32 in which, as shown in FIG. 3, a coil 321 receives radio waves (electromagnetic waves) generated from a reader/writer 31 through a coil 311, transmitting and receiving data signals are generated, and a command transmitted from the reader/writer 31 is processed.
The contactless IC card includes a contact type having the communication distance of about few mm to 10 mm, a proximity type having the communication distance of tens mm, and a remote type having the communication distance of tens cm to few m. Among them, the contact IC card has the international standard ISO10536-2 in which the location and shape of the coils and the electric characteristics are defined.
According to the standard ISO10536-2, as shown in FIG. 3, page 2, ISO/IEC 10536-2:1995(E), two coils are arranged at an interval of 22 mm in a card and the inner size of the coils is defined as (11.6 mmxc3x974 mm).
In order to reduce thickness, an IC card in which antenna coils are formed by printing a conductive paste (for example, silver paste) or the like on a PET film is used. As conventional techniques of the IC card obtained by printing the conductive paste, there are techniques described in Japanese Patent Application Laid-Open No. 8-216570, Japanese Patent Application No. 7-120237, and the like.
The method of forming the antenna coil of the IC card by printing the conductive paste (for example, a silver paste) or the like on a PET (polyethylene terephthalate) film of the conventional techniques have a problem that the conductance, that is, the value of resistance of the coil is larger than that of a coil made of a general copper wire and that of an etching coil on a printed board by one digit or more.
Specifically, in a coil having about 20 turns, although a direct current resistance of a coil formed by copper foil etching is 10 xcexa9 or less, the resistance of a thick film printed coil formed by printing the silver paste or the like is 100 to 200 xcexa9. When power is received and a current flows, if the direct current resistance of the coil is large, the coil itself consumes the power. Consequently, a loss occurs and power efficiency deteriorates. It is therefore important to reduce the resistance of the thick film printed coil by widening the pattern line width of the coil as much as possible.
The coil is printed on the PET film in order to reduce the thickness of the card in the conventional techniques. When coils are printed on both of the surface and rear surface in order to increase the number of turns of the coils, there is a problem such that the antenna coils themselves have a self resonant frequency by a floating capacity (capacitor) occurring between the coils on the surface and rear surface and L (reactance) of the coils and an adverse influence may be exerted on a transmission frequency band. Specifically, the self resonant frequency by the floating capacity when the silver paste coils each having about 20 turns are formed on the PET film having the thickness of 50 xcexcm is few MHz to tens MHz. Since the power and the communication frequency of the contact IC card conforming to ISO10536 are defined as 4.91 MHz, the self resonant frequency is a problem.
It is an object of the invention to provide a contact IC card in which a low-resistance antenna coil is formed by a conductive paste.
It is another object of the invention to reduce the direct current resistance and the floating capacity when an antenna coil in a card is formed by using a conductive paste in a contact IC card, especially, according to ISO10536 standard.
In order to achieve the objects, according to the first feature of the invention, as means for reducing the direct current resistance of the coils, means for partially widening the pattern line width of the coil in parts having dimensional room when the coils are formed is provided.
The second feature of the invention is realized in such a manner that when the coils are formed in two layers on the surface and the rear surface, as means for reducing the capacity between the coils, the coil on the surface and the coil on the rear surface are arranged so as not to be in overlapped positions and the wiring pattern of the coil on the rear side is arranged between the patterns of the coil on the surface.
The features of the invention will be more clearly described as follows.
According to a fundamental feature of the invention, as means for reducing the direct current resistance of the coil in a predetermined dimension, coupling areas are formed in the central parts on the surface and the rear surface of coil forming areas having predetermined dimensions on an insulating film, and antenna coils consisting of a pair of coils on the surface and the rear surface which have the turns in the same direction when seen from the outside and are connected via a though hole in an end part of the coupling areas are formed by a thick film printing method.
According to the feature, the low-resistant antenna coils each having the large number of turns can be formed in the coil forming areas of the predetermined dimensions. Since leads of the surface and rear surface coils formed so as to face each other on the surface and the rear surface of the insulating film are located on the outside of the coils, no leads traversing the coils are formed. Both of the pair of surface and rear surface coils can be formed in almost the same pattern and in the same winding direction on the insulating film, so that it is advantageous also from the viewpoint of manufacturing.
According to another feature of the invention, by forming two or more pairs of the surface and rear coils on the insulating film, connection between the pairs of coils (antenna coils) and external circuits and connection between the antenna coils can be performed on the outside of the coils.
According to another feature of the invention, in the fundamental feature, the coil forming area is a rectangle and the line width of the coil pattern in the longitudinal direction of the coil forming area is formed so as to be wider. According to the feature, the direct current resistance of the coil can be further reduced.
According to further another feature of the invention, in the fundamental feature, the patterns of the surface and rear surface coils of the pair of coils are formed so as to be deviated from each other at a half pitch. According to the feature, the floating capacity between both of the coils can be remarkably reduced.
According to the invention, in a contactless IC card in which coils are printed by a conductive paste, the direct current resistance of the antenna coils can be reduced and the adverse influence on the communication by the self resonance of the coils can be reduced, so that there is an effect that the transmission efficiency of power and signals is improved.
The above and other objects and features of the invention will become more apparent from the following description of the embodiments with reference to the accompanying drawings.